I just got an RB-67 Pro-SD, with two 120 roll film backs. Both have a minor issue with the edge of the negative frame showing fogging. The odd part is that this is between frames, not at the top or bottom. The backs are the late type for the SD, and I cannot find anything wrong with the seals in either the backs or the camera.

Is this typical for RB backs? While the edge fogging is more of a nuisance than anything else, the image area on one of the frames was clearly light struck and I'm not going to trust it until I figure out what is going on.

Also check the seals around the dark slide slot. Since the film is light struck as you described, it may be happening when the film is "parked" either before or after you've advanced the film. As a rule, I never remove/replace the dark slide unless I'm in the immediate act of shooting, and I try to shield the roll film holder from direct sun at all times, either by draping the dark cloth over the camera, or at least keeping the back shaded by my big head or other convenient body part when advancing the film.